1. Field of the Invention
The present invention relates to communication. More particularly, the present invention relates to a novel and improved method and apparatus for determining position of a remote terminal in a wireless communication system, wherein repeaters are detected and compensated.
2. Description of the Related Art
Wireless communication systems are widely employed to support communication for a large number of users. Such systems include CDMA, TDMA (e.g., GSM), and other commonly deployed systems. In a wireless communication system, a user on one remote terminal is able to communicate with another user on another remote terminal (or a wireline unit) via a wireless link to a base station. Each base station is designed to coordinate and facilitate the communication between the remote terminals within its coverage area.
Some wireless communication networks employ repeaters to provide coverage for designated areas within the network or to extend the coverage of the network. For example, a repeater may be used to cover a particular region within a network not covered by a base station due to fading conditions (i.e., a hole within the network). Repeaters may also be used to extend coverage into rural areas (e.g., along a freeway) that are outside the coverage area of the base stations.
A repeater is a high-gain bi-directional amplifier placed in a network to receive, amplify, and retransmit a modulated signal. On the forward link, a signal from a “donor” sector (also referred to as a serving base station) is provided to the repeater via a directive antenna or a cable (e.g., a coaxial or fiber optic cable). The repeater then filters, amplifies, and retransmits the donor signal to the remote terminals in the repeater's coverage area. Correspondingly, on the reverse link, the repeater receives signals from the remote terminals within its coverage area, conditions and retransmits the signals to the base station.
Besides facilitating communication between users, a wireless communication system may be designed with the capability to determine the position of a remote terminal. In fact, the Federal Communications Commission (FCC) has mandated support for an enhanced emergency 911 (E-911) service whereby the location of a remote terminal in a 911 call is required to be sent to a Public Safety Answering Point (PSAP).
For position determination, a remote terminal within a wireless communication system typically measures the arrival times of the transmissions from a number of base stations. The differences between the signal arrival times can be computed and translated into pseudo ranges, which are then used to determine the position of the remote terminal.
Various challenges are encountered in measuring the signal arrival times in a network that employs repeaters. These repeaters introduce additional delays in the remote terminal's time measurements, with the amount of additional delays being unknown in many instances. The additional delays typically cannot be accurately compensated for by the network because it may not be known with certainty whether or not a remote terminal is under the coverage of a repeater. This uncertainty in the sources for the time measurements can result in an inaccurate estimate of the remote terminal's position and/or an increase in the processing required by the remote terminal to determine its position.
Therefore, it is highly desirable to develop techniques that can detect whether or not a remote terminal is under the coverage of a repeater, and to possibly account for the additional delays introduced by the repeater, in determining the position of the remote terminal. These techniques may lead to improved accuracy in the estimated position of the remote terminal and may further reduce the amount of processing required for position determination.